The invention relates generally to the motion analysis of non-rigid bodies, and more particularly, to systems and methods for recovering material properties of non-rigid bodies through vision-based motion analysis and finite element modeling.
The recovery of material properties of non-rigid objects has many important applications in the medical and industrial arts. For example, non-rigid objects include skin, tissue, rubber, and plastic, just to name a few. Situations often arise where it is desirable to know the material properties of a non-rigid object such as during, for example, medical treatment or quality control during manufacturing processes. These situations include, for example, the detection of abnormalities in the non-rigid objects. Nevertheless, it is sometimes difficult to know the material properties because some non-rigid objects can only be investigated non-invasively. Or said another way, to invasively investigate the non-rigid objects would cause damage to the objects themselves. Additionally, most current non-invasive investigations are quite subjective.
In response to these difficulties, attempts have been made to use non-rigid motion tracking of the objects under investigation. Methods for non-rigid motion analysis are based on having complete, physically-based, mathematical models of the non-rigid object undergoing the motion tracking. However, in many cases the information required to generate a complete physical model of the non-rigid object is often not available. Attempts at generalizing and simplifying such unknown material properties or information compromises the advantages gained from using such models. Therefore, it is desirable to provide a method for accurately analyzing the material properties of non-rigid objects that does not suffer from these disadvantages.
According to one embodiment of the present invention, a method of analyzing material properties of a non-rigid body is provided. The method includes the steps of: establishing a plurality of three-dimensional point correspondences of the non-rigid object in an unstressed and stressed state; from the plurality of point correspondences, generating a finite element model of the non-rigid body having initial material properties and generating a finite element strain distribution; detecting abnormal areas of the non-rigid body by comparing finite element strain levels from the strain distribution; and determining at least one material property of the abnormal areas. The step of determining at least one material property of the abnormal areas includes a plurality of sub-steps such as, for example: establishing a plurality of boundary point correspondences from the plurality of point correspondences; inputting the boundary point correspondences into the finite element model for generating a predicted set of three-dimensional point correspondences of the non-rigid object in the stressed state; and refining the at least one material property based on a comparison of the predicted set of point correspondences and the set of point correspondences of the non-rigid object in the stressed state until the predicted set of point correspondences and the set of point correspondences of the non-rigid object in the stressed state are within a minimum difference.
The step of establishing a plurality of three-dimensional point correspondences of the non-rigid object in an unstressed and stressed state also includes one or more sub-steps such as for example: determining a first set of three-dimensional point correspondences from a plurality of grid lines overlying the non-rigid object in the unstressed state and range information and determining a second set of three-dimensional point correspondences from the plurality of grid lines overlying the non-rigid object in the stressed state and range information. The step of detecting abnormal areas of the non-rigid body by comparing finite element strain levels from the strain distribution also includes one or more sub-steps such as, for example: identifying finite elements having low stress and identifying finite elements having high stress. The step of refining the at least one material property also includes one or more sub-steps such as, for example: changing the elasticity or geometry of the finite elements. Other embodiments of the present invention include a computer readable medium having computer program logic recorded thereon for determining at least one material property of a non-rigid object through one or more the aforementioned steps.
The present invention is applicable to, for example, burn scar assessment, natural and man-made elastic materials, and human hand modeling. Human hand modeling according to the present invention provides a valuable tool for the analysis of Repetitive Stress Injury by analyzing the hand positions on devices such as keyboards that may result in excessive strains on the hand. The loads on the tissue surrounding the wrist joint are analyzed to determine and define safe exposure limits.
It is therefore an object of the present invention to provide a system and method for recovering material properties of non-rigid objects when only partial information relating the material properties is available.
It is a further object of the present invention to provide a system and method for the non-invasive analysis of scarred skin.
It is another object of the present invention to provide a system and method for recovering missing geometry in a non-rigid object.